1. Field of the Invention
The present invention concerns improvements to the measuring methods disclosed in French patents Nos. 2 636 731 and 2 646 904 respectively filed 16 Sep. 1988 and 9 May 1989.
2. Description of the Prior Art
In these methods the transverse cross-section plane of a cylindrical object whose diameter is to be measured is scanned at constant speed by a laser beam which remains parallel to a predetermined direction and the time for which said beam is intercepted by the object is measured.
The application of these methods to measuring the diameter of a cigarette usually requires that the measurement is performed in a plurality of directions in the transverse cross-section, the cigarette being rotated about its axis for this purpose and the mean value of its diameter being calculated.
The second of the aforementioned patents further provides for moving the cigarette in translation parallel to its axis in order to measure its diameter in a plurality of transverse cross-sections to allow for any axial variations due, for example, to the presence of a torn paper fragment projecting from the body of the cigarette.
In theory the presence of any such projection increases the measured diameter.
It has been found that in some cases, in practise in the presence of "fluff" (defects inherent to the structure of the paper in which the tobacco is wrapped), the mean diameter measured in one transverse cross-section is actually less than the real value, by as much as 10%.
An object of the invention is a method which eliminates this drawback and makes it possible to eliminate totally the effects of any kind of foreign bodies or asperities on the surface of a body whose transverse dimension is to be measured.
Another object of the invention is a method of measuring a plurality of dimensions in a common direction on a transverse cross-section having surface discontinuities, for example, internal voids.